Energy storage technology is incontrovertibly one of the great challenges in the modern society facing environmental and ecological concerns, and the lithium ion battery is regarded as one of the most important energy storage devices due to its extensive applications in many areas including portable electronic devices, electric vehicles and implantable medical devices. As the heart of clean energy devices, the development of energy storage materials holds the key to the new generation of energy storage devices in the 21st century. Nanostructured materials have attracted increasing interests in the field of energy materials due to superior electrochemical properties benefited from the unique nanostructure, such as nanoscale dimension, high surface area and large structural freedom which could provide high energy and power density while holding the mechanical integrity and chemical stability after many intercalation/deintercalation cycles.
Vanadium oxide is a multi-functional material which has extensive applications in various fields. Since its first investigation as a battery material for lithium ion batteries over 40 years ago, it has been discovered that during Li+ ions intercalation vanadium pentoxide (V2O5) possesses high specific electrochemical capacity (theoretical capacity 450 mA h g−1) with four phase transitions which involves five successive phases of LixV2O5 (0<x<3): α (x<0.01), ε (0.35<x<0.7), δ (0.9<x≦1), γ (0<x≦2) and the irreversible ω (x>2). Although the Li-ion intercalation voltage is lower than LiCoO2 or LiMn2O4, V2O5 has still been regarded as one of the most popular cathode candidates for Li ion batteries due to these advantages: V2O5 provides higher energy and power density than LiCoO2 and LiFePO4, is easier and more controllable fabrication method than LiMO2 (M=Ni, Mn, Co, Fe), and has higher capacity and better cyclic stability than LiMn2O4. There are various processing methods to prepare nanostructured vanadium pentoxide with high electrochemical performance for lithium ion batteries: self-assembled V2O5 hollow microspheres from nanorods; V2O5 submicro-belts from sol-gel precursor combined with hydrothermal method; Electrospun V2O5 nanofibers; Electrostatic spray-deposited V2O5; co-precipitated macro-plates V2O5 from water/ethanol media and V2O5 nanowires from chemical vapor transport. These nanostructured vanadium pentoxide materials have shown improved electrochemical performance in comparison with conventional cathode materials for lithium ion batteries, however due to the high cost of fabrication and complicated processing method, the broad industrial applications of such nanomaterials are limited.
Therefore, what is desired is an improved method for forming V2O5 that provides V2O5 films with superior properties when incorporated as cathodes in lithium-ion batteries.